Stringent emissions standards in Europe and North America are requiring automakers to reduce emissions produced by vehicles. Various technologies have been developed to reduce these emissions.
For instance, some diesel engines exhibit high levels of nitrogen oxide (NOx) emissions. Selective catalytic reduction (SCR) approaches have been used to convert nitrogen oxides into nitrogen, N2, and water, H2O.
In SCR approaches, a reduction delivery unit (RDU) is used to inject a Diesel Exhaust Fluid (DEF) reductant into the exhaust stream of an engine. For example, urea is added to the exhaust gas stream by the RDU and various byproducts such as carbon dioxide and water are formed. Ammonia is a desired bi-product and in conjunction with a catalyst converts the nitrogen oxide (NOx) into harmless water and nitrogen.
The RDU has a fluid injector that is in some cases liquid cooled by a liquid jacket. A conventional RDU fluid injector has a fluid outlet which extends into or is otherwise exposed to the flow path for the engine's exhaust in the exhaust pipe. The liquid jacket of a conventional liquid-cooled RDU is also exposed to flow path of the engine's exhaust. The relatively high temperature of the engine exhaust has been seen to adversely affect the RDU fluid injector and the operation thereof. The temperature gradient between the exhaust gases, mounting flanges and the RDU has been known to accelerate the formation of deposits that affect spray quality, thus affecting the ability to convert nitrogen oxides into N2 and H2O.